KI 1113 How to classify and protect e-mails in Outlook
You can select to show the band to have the tabs available at any time when writing an e-mail.
If you choose to send the e-mail as Confidential, the recipient will not be able to copy from, print or forward your email.
Unprotected Office documents associated with the e-mail automatically inherit the restrictions. If your attachment is not an Office document that supports this inherited protection, you must protect the file before attaching it to the e-mail. You can then assign the specific usage rights you need for the file.
We would recommend sharing documents instead of sending them as attachments to e-mail! (Please see KI 0620 How do I cooperate on a file in OneDrive? for instructions.)